>I'd use a libre client even if they are big, slow and uglyThe smallest, fastest and most beautiful clients are libre. You don't even need a bloated GUI.
I don't quite understand what you're doing but you can write a one-liner loop to do that renaming in the terminal or if that's not your forte, there's plenty of GUI renamers to do it for you, e.g. gprename.
for i in *.lut; do mv $i `basename $i .lut`.part; done
